This invention relates to plasma devices. In particular, this invention is a divertor for removal of unwanted charged particles from a plasma.
A noticeable feature of most models both built and proposed for plasma systems is some form of divertor. This is an apparatus that operates to remove unwanted particles from the plasma while interfering as little as possible with the maintenance of the plasma. The unwanted particles may be impurities that are sputtered from the walls of the plasma device or they may be escaping hot particles which would bombard the wall in the case of a plasma device that is intended to be some form of a reactor. In either case, the unwanted particles tend to cool the plasma by their presence and it is desirable to remove them from the plasma to maintain the plasma in a desired state. This is a particular problem in the Tokamak which is a plasma device in which the plasma is confined in a toroidal region by a combination of magnetic fields that are toroidal and poloidal. The term "poloidal" refers to magnetic fields in the plasma region that are in a plane containing the axis of the toroid. These fields contribute to the stability of the plasma. It is well known that a plasma in a purely toroidal field configuration is not stable. The addition of a carefully calculated poloidal field provides the stability that is a principal feature of the Tokamak. This is accomplished by creating a pattern of magnetic flux lines in the center of the plasma region that adds to the magnetic flux that is applied to confine the plasma in the toroid and also to the magnetic flux generated by the plasma itself to create an average minimum of magnetic field within the plasma or to create shear in the field. Such an average minimum serves as a collection region both for particles of the plasma and for unwanted charged particles, the impurities described above.
Early attempts at removing unwanted particles from plasmas were characterized by divertors such as those used on the Stellarator, an early twisted toroidal plasma device. Divertors on the Stellarator applied a small opposing magnetic flux near the outside of the twisted toroid to bend some of the outer toroidal flux lines in a loop. That loop was passed through an enclosure that included a collecting surface. Charged particles that were free to travel along the outer flux lines were trapped on the collecting surface and thereby removed from the plasma. However, the divertor in the Stellarator distorted the confining magnetic fields. An ideal divertor would not perturb or destroy the symmetry of the confining magnetic fields of the plasma device and would promote the quick removal of particles from the plasma edge.
It is an object of the present invention to provide a divertor for a plasma confinement system such as a Tokamak.
It is a further object of the present invention to provide quick and controllable passage of particles out through the diverter region.
It is a further object of the present invention to extract impurities from the plasma in a plasma confinement system such as a Tokamak by the use of crossed fields.
It is a further object of the present invention to extract impurities from a plasma without perturbing confining magnetic fields.
Other objects will become apparent in the course of a detailed description of the invention.